The present application relates to the extraction of catalyzing material from polycrystalline diamond tables.
Drill bits and components thereof are often subjected to extreme conditions (e.g., high temperatures, high pressures, and contact with abrasive surfaces) during subterranean formation drilling or mining operations. Polycrystalline diamond table is often used at the contact points between the drill bit and the formation because of their wear resistance, hardness, and ability to conduct heat away from the point of contact with the formation.
Polycrystalline diamond table is formed by mixing diamond particles and a catalyzing material (alternately referred to in the art as a catalyst) (e.g., cobalt, nickel, iron, Group VIII elements, and alloys thereof) followed by high-pressure, high-temperature (HPHT) sintering. The catalyzing material facilitates bonding between the diamond particles into a larger, polycrystalline diamond table. Once formed, the catalyzing material remains within the body of the polycrystalline diamond table.
The catalyzing material in the polycrystalline diamond table can cause degradation of the polycrystalline diamond table when the catalyzing material is again heated in the absence of an inert atmosphere, for example, during brazing to attach the polycrystalline diamond table to a hard composite substrate when forming a cutter, during brazing to attach the cutter to a drill bit, and during a drilling operation. Specifically, the catalyzing material can cause cracks due to a higher coefficient of thermal expansion compared to diamond and also cause graphitization at diamond grain boundaries. The fractures and graphitization weaken the polycrystalline diamond table and may lead to a reduced lifetime for the drill bit.
To mitigate fracturing of the polycrystalline diamond table, it is common to remove at least some of the catalyzing material, and preferably most of the catalyzing material, from the interstitial spaces of the polycrystalline diamond table before exposing the polycrystalline diamond table to elevated temperatures. Polycrystalline diamond table having a substantial amount of the catalyzing material removed is referred to as thermally stable polycrystalline (“TSP”) diamonds. The quality and thermal stability of the polycrystalline diamond table generally increases with greater removal of the catalyzing material.
Catalyzing material is typically removed by leaching, which commonly includes exposing the diamond to strong acids at elevated temperatures that dissolve the catalyzing material. However, this process can be inefficient, often taking days to remove a substantial amount of the catalyzing material.